A 32-hour workweek is better but the 36-hour is more politically viable.
Memes can be intractable. Beliefs are sometimes impossible to alter once they're lodged in someone's mind. The 40-workweek is one of them. The modern workweek was created during the Great Depression for the same reasons that a 36-hour workweek is appropriate now.
Imagine a four-day workweek. The average American would have 52 three-day weekends each year. Gas consumption would drop. Traffic reduced. A broader distribution of income creates a healthier economy.
I've known this history for about twenty years and formulated this workweek theory sometime around 2007:
1) Work is finite
2) In a productive economy, work shrinks over time
Economic depressions are a tragedy of the commons. The 40-hour workweek was a coarse adjustment to force a rough balance between production and consumption at that time, putting the economy back on an even keel.
Empirical evidence - well, there's the Great Depression, when the workweek shrank from 48 to 40 hours, a 16% decrease. But where did the 48-workweek come from?
From the Industrial Revolution and the Long Depression (1873 to 1896).
After the Civil War, the Industrial Revolution split work into two categories - skilled and unskilled, creating a 48 hour and a 60 hour workweek. The workweek declined something like 10-15% during that period, re-merging as a standard 48-hour week in the 1890s.
We can work out a simple math model, too.
Work is finite because consumption is finite.
Consumption is finite because our TIME is finite.
In an efficient economy, what we produce equals what we consume.
1) Production = Consumption. (P = C)
Now define our model as one worker and our time period as one week.
Our worker has 168 hours per week, of which 56 are spent on sleep, so hours of production + hours of consumption = 112. We also know today's workweek is 40 hours.
2) P Hours + C Hours = 112
3) (P Hours) X (Rate of P) = (C Hours) X (Rate of C)
4) (40 hours) x (Rp) = (72 hours) x (Rc)
What happens in a "productive economy"? (Rate of P) increases.
So (Rate of C) must increase to maintain equilibrium.
Workers must consume an ever-greater amount of goods in the SAME CONSUMPTION PERIOD. We could buy a new car and new house every day but marginal utility says that people will find other uses for their time than consuming for the sake of consuming. Sales are bounded by our time. If you want more sales, you need more customers.
Henry Ford realized this almost one hundred years ago when he introduced the 40-hour workweek just prior to the Great Depression. But today's capitalists aren't as smart.
That's why a 36-hour workweek fixes a broken economy. Existing workers get something of value (their time) and employers must hire several million under-employed people, re-distributing spendable income across a broader population (more customers, hello?). As it is now, the government taxes workers to force that re-distribution; workers resent those taxes as there's no direct value for them, and it rewards non-workers with income for no effort.